Automatic external defibrillators (AEDs) are defibrillators that are designed to be operated by users with minimal training. Because AEDs can be used by non-medical personnel to treat sudden cardiac arrest (SCA), they are being deployed in a myriad of locations outside of traditional medical settings. As a result, more and more non-medical establishments are purchasing AEDs for deployment in their environments. AEDs are typically powered by stand alone battery systems.
AEDs are typically standby devices that are used infrequently and that remain in storage for long periods of time. This standby storage time can be on the order of months or even years. Minimizing power consumed by the AED while it is in standby mode during storage may extend the battery life of the system and reserve battery power for rescue attempts using the AED.
Since AEDs are in standby mode for long periods of time, knowing the operational status of a standby AED is very important. The operational status of an AED can be determined by various internal self tests. These tests may cover general operations, battery life, memories, software, etc. The results of these tests can be communicated to a user via visual or aural indicators even while the AED is in a low power standby mode. In such a system, there can be a status circuit or apparatus inside the AED that can report the status of the AED system. More generally, the AED may be referred to as the host system or host device. Various systems other than AEDs have similar low power consumption requirements for status indicators. Such systems may be referred to as host systems or host devices when they include status circuits that indicate the status of the host system.
Status indicators for host systems may be passive or active. An active indicator is one that may require power to be expended for it to continue to indicate, such as an indicator light. A passive indicator may continue to indicate without consuming additional power. For example, an indicator that mechanically changes colors by physically flipping an internal element that can be seen by a user through a window may be a passive indicator. Once the internal element of the passive indicator is physically flipped, it will stay in that state without additional power.
Active indicators can include lights, light emitting diodes (LEDs), video screens, speakers, or buzzers. Active indicators have the disadvantage of continuing to use power over time, but they can allow host status to be more readily determined in a wide variety of ambient conditions. For example, an active indicator may illuminate a green light to indicate that its battery is healthy, or a red light when its battery needs replacement. This repeated illumination of a light requires power, but may be much more likely to catch the attention of a user than a passive indicator would. This may be particularly true if the device is stored in a dark or low-visibility environment.
For battery powered, standby devices, such as AEDs, conservation of battery power is an important design goal. Such systems that use active status indicators have the additional challenge of reducing the amount of power they expend operating the status indicators. Since these devices may be stored, in standby mode, in a variety of environments there are times when the power used for status indication is excessive. For example, if a status light is designed to be bright enough to be seen in a well lit room, it may be much brighter than necessary when in a dark room or when stored in a cabinet, carrying case or car trunk.
Similarly for an aural status indicator, if the volume level of the indicator has adequate magnitude for a noisy environment, such magnitude may be much higher than necessary in a quiet room setting and therefore consume more power than necessary. Because of the importance of conserving battery life in systems with long standby requirements, such as AEDs, there is a need for status indicators that may sense their operating environment and then adjust accordingly either, or both, indicator intensity or indication event frequency.